test_platform: add operator type to BranchFilter

We need the filter to represent branch specs like
">=tot", "<=tot" and "==tot".

BUG=1029994
TEST=NA

Change-Id: I5ab6c6d314af681b6bf1af5e1c95acc2dd65b944
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/2025979
Tested-by: Xinan Lin <linxinan@chromium.org>
Reviewed-by: Alex Zamorzaev <zamorzaev@chromium.org>
Commit-Queue: Alex Zamorzaev <zamorzaev@chromium.org>
3 files changed